1. Technical Field
The present invention generally relates to an apparatus and method for removing plaque and decay tissue, commonly known as dental caries, using laser radiation. More particularly, the present invention relates to an apparatus using ultraviolet radiation and a coolant to ablate a desired material from a tooth without generating excess heat at the target site or surrounding areas.
2. Discussion
As is generally known in the art of dentistry, conventional drilling machines for treating dental caries such as plaque and decay tissue can be inaccurate and painful. Therefore, it is desirable to replace or support conventional drilling machines with lasers in order to achieve a more accurate and painless treatment of caries. However, laser irradiation processes currently available often produce charring on the target surface and surrounding areas due to laser generated heat. The blackened char tissue effectively blocks the laser radiation thereby preventing it from reaching biological tissue thereunder. Thus, charring due to excess heat interrupts the ablation process.
Excess heat may also produce cracks in the tooth surface and damage the nerve system and other pulp structure in the pulp chamber irreversibly. Accordingly, laser treatment of hard tissue, including caries removal, has not yet achieved practical dental application due to the thermal damage related to laser generated heat. Therefore, it is desirable to provide an apparatus and method for treating dental caries using laser irradiation which does not generate sufficient heat to cause thermal damage.
In conventional dental surgery using drilling machines, water is commonly used to dissipate heat and remove debris from a work area. Water has also been used in laser dental surgery for the removal of excess heat after irradiation of a target area with laser pulses. For example, Vassiliadis, et al. (U.S. Pat. No. 4,940,411) discloses a dental laser method using a Neodymium doped Yttrium-Aluminum-Garnet (Nd:YAG) infrared laser.
Vassiliadis, et al. teach spraying water on a tooth following each laser pulse. Thereafter, the tooth is dried prior to a subsequent pulse from the laser. This teaching conforms with studies concerning infrared laser treatment of dental caries which stress the need to keep the tooth dry during delivery of laser pulses in order to minimize attenuation of the laser by the water. During infrared laser treatment, water has to be nearly absent due to the laser being strongly absorbed. A drying means, such as an air sprayer is generally used to dry the tooth surface before a subsequent laser pulse is applied.
On the other hand, Wolbarsht, et al. (U.S. Pat. No. 5,267,856) discloses that a thin layer of water entering the surface pores or chemically held on the surface of the tooth can enhance the removal rate of desired material when using an Erbium doped Yttrium-Aluminum-Garnet (Er:YAG) infrared laser. Wolbarsht stresses that the water should not be permitted to remain pooled on the tooth surface in this process because of the inability of the infrared radiation to penetrate thick layers of water effectively. Therefore, the thickness of the water layer must be critically controlled during the process.
One problem with infrared lasers is that they are not selective in treating carious tissue without effecting dentine and enamel. Furthermore, infrared laser light cannot penetrate through water except over relatively short distances. Therefore, infrared processes exclude the use of a relatively thick layer of water spray to achieve effective cooling. Accordingly, it is desirable to provide a laser which is selective in removing carious material and which penetrates thick layers of water. In this way, water can be sprayed on the tooth surface in a non-critically controlled manner such that it may pool or form a thick layer thereon which is effective to prevent charring of tissue. Furthermore, the thick layer of water provides a greater cooling effect and allows use of greater laser fluence which improves the ablation process rate.